Vibratory screening device



Nov. 22, 1938. .1. A. FLINT VIBRATORY SCREENING DEVICE Filed Dec. 12, 1934 3 Sheets-Sheet 1 l/EN TOR: James A. F0777;

Nov. 22, 1938.

J. FLINT 2,137,753

VIBRATORY SCREENING DEVICE Filed Dec. 12, 1934 3 Sheets-Sheet 2 ATT'X Nov. 22, 1938. J. A. FLINT VIBRATORY SCREENING DEVICE Filed Dec. 12, 1954 5 Sheets-Sheet 3 James Af /D77? Pa tented Nov. 22, 1938 UNITED STATES PATENT OFFICE VIBRATORY SCREENING DEVICE .lames A. Flint, Bexlcy, Ohioyassignor to The Traylor Vibrator Company, a corporation of Colorado Application December 12, 1934, Serial No. 757,159

5 Claims. (01. 209-311) This inventionrelates to a vibratory screening are also welded to the channel members It: and device, particularly of the multiple screen type. a their DP te e ds- An object of the invention is to provide a Adjacent t e p 01' eac o the P plates screening device of the multiple screen type in 13 is a p member Preferably formed which the screens are vibrated with respect to The Ded pl o et With e 6 ea h th r provide h t is herein t d a channel members l6 and H, in cooperation with action screen. the reinforcing tubes 8 and the side plates l2,

Another object fth i v ti 1 t provide form a sill or deck across which is adapted to be screening device having a motor for. vibrating a stretched a wire mesh screen 20. The rubber cap I plurality of screens along n axi making an acute members l9 provide a cushion between said screen 10 angle with a surface of each of the screens. end the Ped P ates I3 p f t u due Still another object of the invention is to pro- Wee-ring Said Screen h Side d e f Sa d vide anew and improved mounting and tensi screen 20 rest on flanges 20a extending inwardly ing means for a wire mesh screen. from the Side p es p 5 Other objects of the invention will appear here- Extending longit y of v pp een inafter, the novel features and combinations beassembly is P of c ndric P p 2| d ing set forth in the appended claimg 22 adapted to be received, respectively, in the slots In the drawings; II and I5. Said slots l4 and I5 provide bearings Fig. 1 is a side elevational. view of the device for the ends of Said Pipes 2| d which e d l cgmprising my invention; project laterally from the side plates l2, and ro- 20 Fig, 2 i a sectional view of t device t n tatably maintain said pipes between said plates along the line 2 2 of Fig. 1 looking in the direcl2. Said pip s 2| and 22 a e pr t each ti n of th arr w end with heads 23 and 24, respectively. Said Fi 3 i a sectional View of t device taken heads 23 and .24 have central drill holes 25 and i gt line 3 3 of Fig 2; 26, respectively, adapted to receive inwardly-pro- 26 Fig 4 is an enlarged sectional detail showing jecting pins. carried by the brackets 21 and 28, one wire mesh creen clamping means which may respectively, which are attached to the be employed; and ends of the plates l2, as by nuts and bolts 29 and Fig. 5 is an enlarged sectional detail showing a respectively Said cylindrical Pipes and 22 modifi d f f wire mesh screen clamping have lever arms 3| and. 32, respectively, rigidly 30 means. attached thereto at each end, which have notched Referring particularly to Figs. 1, 2 and 3 of the terminals 33 and respectively adapted drawings, there is illustrated a vibratory screenceive hooked bolts 35 and 35 yieldably held in ing device which is herein designated as or the taming 37 and 3 of brackets 39 and 5 rea tion ty e This device comprises an upper the Side plates '2, through adjustable vibratory screen assembly l0 and a lower vibra- Spring bearing means and The wire mesh tory Screen assembly The upper Screen screen 20 is attached at one end to the pipe 2| by sembly l0 comprises a deck formed by a pair of clamping means illustrated in detail in Figs. 4 laterally disposed side plates 12 between which and 5 hereinafter der1bed at the other end, extend a plurality of lateral Z-shaped plates I3 110 the pipe 22 by similar attaching means. 40

which are rigidly attached at their opposite ends It is manifest that the cylindricalipipes 2| and to said Side plates n as by we1ding Adjacent 22 are rotatably supported in the bearings of the the bottom ends, both forwardly and rearwardly plates m by the $10,158 and and may of the Side plates '2 are provided the open end be rotated therein by turning of the lever arms 3 s1 Ots 4 and '5 respectively, for a purpose which 3| and 32 under the control of tensioning means will hereinafter described. 4| and 42. By this construction,'the screen 20 Positioned adjacent said slots l4 and I5 is a 33 2 g g gg i ggg gg ggigg :32:32: pair of laterally'extenqing P t members I5 also provid s for ready removal of the pipes 2| a e -'f h h ngldly attached at and. 22, for attaching a new screen thereto or i opposlte m slfle plates as by placing a different mesh screen on the deck. v Extendmg longltudmelly q upper It is to be noted that the tops of the plates l3 e y Screen e e y is a De 1 do not lie in a single plane but, as viewed in secforcmg tubes H! which pass through the Z-shaped tion in Fig. 3, form the screen 20 to an areuate 5 pla es I3 and are we theretod tubes 1 configuration. This provides ior the proper mainwelding, and form reinforcing means for said plates l2.

Extending transversely between the side plates l2 and rigidly attached thereto at its ends, as by welding, is a channel member 46. The side plates of said channel member 48 are adapted to .receive the head 41 of an armature shaft 48 of an electric motor or vibrator 49. Said head 41 is rigidly attached to the side plates of said channel member 46, as by nuts and bolts 50.

Said head 41 is of hollow construction to reduce.

theweight thereof and is provided with a pair of central reinforcing webs 5|. Cooperating apertures 52 and 53 are provided in said channel member 48 and head 41, respectively, to provide access to the interior of said hollow head 41.

The motor or vibrator 49 comprises an armature 54 of laminated iron rigidly secured to the' armature shaft 48 by the bracket 55 rigidly attached thereto, as by nuts and bolts 56.

The field structure for said motor 49 constitutes a U-shaped core 51 built of laminations, the legs of which are surrounded by field windings 58. Said field windings 58 and the core 51 are rigidly mounted upon the brackets 59, which brackets are, in turn, adjustably mounted upon the U-shaped frames 88 by adjustable bolts 6| extending through the split base of said frames 68 and attached to the brackets 59 by spaced nuts 82. The bolts 6| may be adjusted with respect to the frames 88 by releasing the clamping bolts 88 and screwing said bolts 6| to any desired position. Said bolts 6| may thereafter be maintained in said position by screwing home the bolts 63. Thereafter spaced nuts 82 may be adjusted with respect to said bolts 9| to position variably the brackets 59 which, in turn, determine the position of the field structure of said motor 49 with respect to the armature 54. This adjustment provides one means to control variably the amplitude of vibration of the armature 54 with respect to the field of said motor 49.

The U-shaped frames 65 are provided with feet 64 which are adapted to be attached to the upwardly-projecting bosses 55 carried on the laterally-extending channel bars 88 by the screws 61 extending through drill holes in said feet 64 and threaded in apertures in said bosses 85. Rigidly attached between said channel bars 86, as by welding, is a pair of heavy cast rings 88. Said rings 88 are provided with upper and lower inwardly-projecting bosses 69 and 10, respectively. Rigidly clamped between said bosses 89 and III of said rings 88 is a plurality of stacked spring bars ll preferably formed of spring steel and held in rigid clamping position to said rings 68 by clamping plates 12, which clamp the ends of said ,bars against the lower bosses 18 under the action of the studs I8. That is, by screwing down the studs 13, the plates 12 clamp the ends of the spring leaves between said plates 12 and the bosses II of said rings 68.

The armature shaft 48 is provided with a lateral opening I18 through which said spring leaves ll extend. Projecting inwardly 0.! sa d opening 49 away from the field structure.

"3 and adjacent the top thereof is a boss 14 forming a part of said armature shaft 48. Within said opening I13 and adjacent the bottom thereof is a clamping plate 15 which is adapted to be clamped against the spring leaves H and thereby clamp said spring leaves adjacent their centers between said clamping plate 15 and the boss 14 under theaction of the threaded studs 16.

The clamping plate 15 may be provided with a bolt 11 threaded therein and extending through an opening in the web 18 of said armature shaft 48 around which-extends a coil spring 19. bolts 11 and coil spring I9 are adapted to maintain the plates 15 within the opening |'|3 before the spring leaves II are clamped rigid in said opening, the coil spring 19 allowing free movement of said plate 18 under the action of the stud 18 in performing the clamping operation.

It is thusseen that the field structure of the motor 49 isrigidly attached to the ends of the spring leaves 1| while the armature of said motor is rigidly attached to the central portion of said spring leaves II. It is therefore obvious that, if the field of said motor 49 is cyclically energized by a source of pulsating current, such as a source of commercial 60-cycle alternating current, there will be a periodic vibration of said armature with respect to said field structure and a consequent periodic deflection and restoration of the spring leaves 7|. It may be stated that this period of vibration has a frequency which is twice the frequency of the energizing source; in the example mentioned it would be 120 cycles per second. This is due to the fact that each half-cycle of alternating current is effective to attract the armature toward the field of said motor 49 and to defiect thereby the spring leaves When the force due to magnetic attraction decreases to zero, the energy stored in the spring leaves ll is effective to move the armature of the motor It is manifest that with the usual commercial alternating current the deflecting forces will pass through zero twice during each cycle of operation.

Rigidly attached to the ends of the channel bars 66 is a pair of downwardly-projecting angle members 88 which extend laterally of the upper screen assembly l8 and are attached to the side plates 8| of the lower vibratory screen assembly through plates 82; said angle members 88, plates 82 and side plates 8| being attached together, as by welding the plates 82 to the side plates 8| and by riveting or welding the plates 82 to the angle members 88. It is thus seen that said lower vibratory screen assemoiy I is rigidly attached to the field structure of the motor and vibrates as a unit therewith while the upper vibratory screen assembly In is rigidly attached to the armature structure of said motor and vibrates as a unit therewith.

Said

- The lower vibratory screen assemblyll is of substantially the same construction as the upper vibratory screen assembly l8 except for the configuration of the side plates 8i. Said lower vibratory screen assembly comprises a deck formed by a pair of laterally-disposed side plates 8| between which'extend a plurality of lateral z-shaped plates l3 which are rigidly attached at their opposite ends to said side plates 8|, as by welding. Adjacent the bottom ends, both forwardly and rearwardly of the side plates 8|, are provided the open end slots l4 and I5, respectively, for a purpose which will be hereinafter described. I

Positioned adjacent said slots l4 and |5' is pair of laterally-extending angle members It clined inwardly-extending plates |9| which form and I1, respectively, which are rigidly attached at their opposite ends to said side plates 8|, as

by welding. Extending longitudinally of the lower vibratory screen assembly II is a pair of reinforcing tubes l8 which pass through the is a cap member l9 preferably formed of rubber.

The Z-shaped plates l3, together with the chan-- nel members I6 and I1, in'cooperation with the reinforcing tubes l8 and the side plates 8|, form a sill or deck across which is adapted to be stretched a wire mesh screen 28'. The rubber capmembers l9 provide a cushion between said screen 28' and the z-shaped plates l3 to prevent undue wearing of said screen 28'. The side edges of said screen rest on flanges 28b extending inwardly from the side plates l2.

Extending longitudinally of said lower screen assembly I] is a pair of cylindrical pipes 2| and 22' adapted to be received, respectively, in the slots l4 and I. Said slots l4 and I5 provide bearings for the "ends of said pipes 2| and 22 which ends project laterally from the side plates 8| and rotatably maintain said pipes between said plates 8|. Said pipes 2| and 22 are provided at each end with heads 23' and 24', respectively. Said heads-23' and 24' are provided with central drill holes 25' and 26, respectively, adapted to receive inwardly-projecting pins carried by the brackets 21' and 28', respectively, which are rigidly attached to the ends of the plate 8|, as by nuts and bolts 29' and 38', respectively. Said cylindrical pipes 2 I and 22' have rigidly attached thereto at each end brackets 3| and 82', respectively, which have notched terminals 33' and 34' adapted to receive hooked bolts 85' and 38 yieldably held in retaining notches 31 and 38 of brackets 39' and 48' rigid with the side plates 8| through adjustable spring bearing means 4| and 42'. 'The wire mesh screen 28' is attached at one end to the pipe 2| by clamping means illustrated in detail in Figs. 4 and 5 hereinafter described, and, at the other end, to the pipe 22 by similar attaching means.

It is manifest that the cylindrical pipes 2I' and I5 also provide for ready removal of the pipes 2| and 22'. It is to be noted that the tops of the plates l3 do not lie in a single plane, but

as viewed in section in Fig. 3, form the screen 'toan arcuate configuration. This provides for' the proper maintaining of the screen 28' against f the cap members IS on said plates l8 when said screen is tensioned and prevents vib'ator'y rovement of said screen with respect to said cap members l9 during vibration of the unit Each of the side plates 8| is provided on its outer surface with a top angle member 43', a bottom angle member 44 and a plurality of transverse reinforcing bars or channel members 45, all of which are formed rigid with said plates 8|, as by welding, and form reinforcing means for said plates 8|.

Said lower screen assembly II is also provided adjacent the side walls 8| with a pair of infianges against which the sides of the screen 28' are adapted to rest. It may be noted that said lower screen assembly including said screen 28', is somewhat wider than the upper screen assembly l8. Said screen 28 therefore effectively receives any material which may-pass through said upper screen 28-.

Rigidly attached to the side plates 8| adjacent the upper'.portion of the lower screen, assembly I I is a plurality of brackets 82 adapted to carry spring leaves 83 each of which is clamped to one of said brackets 82 adjacent one end thereof as by the clamping plates 84 and the screws 85. The other end of each of said spring leaves 83 is attached by clamping plates 86 and screws 81 to one of the brackets 88 rigidlyattached to the bottom portion of the side plates l2 of the upper screen assembly "I.

The side plates 8| of the lower screen assembly II' are provided at one end thereof with supporting eyes 89, said eyes being preferably carried in the top flange of the angle member 43 of said side plates 8|. Flexible mounting means for supporting the device is attached to said eyes 89 and comprises a hooked bolt 98 around which is coiled a coil spring 9|, one end of which rests against a washer under the nut 92 on said bolt 98 and the other end of which rests against the bottom of a cylinder 93, the upper end of which cylinder is attached to a suspension rod 94.

The upper channel bar 68. also carries laterally spaced plates 95 provided with holes 98 adapted to receive selectively the bolt of a clevis '91 which clevis is attached by a,chain link 98 to the hook end of a spring mounting means 99 similar to that cooperating with the eyes 89. A turnbuckle I88 is interconnected with the spring mounting means 99 and a suspension rod |8|. There will, of course, be a pair of suspension rods IM and 94, each of which is adjacent a side of the device whereby said device may be supported.

It is to be particularly noted that, as viewed in Figs. 1 and 3, the longitudinal axis of the motor 49-that is, the axis of vibration of said motor-is disposed at an'angle with respect to the surface of the screen 28 of the upper vibratory assembly l8 and the corresponding assembly of the lower vibratory assembly I By virtue of this construction, said motor 49 in its vibration not only imparts a vibratory movement to the screen 28 which is effective to lift periodically any material on said screens therefrom but is also eflective to impart a conveying action to said particles of material. Where the screens are set at an inclination to the horizontal, there will, of course, be a natural gravity feed operating on any material on said screens which will tend to move the material from the upper to the lower portion thereof as said screens are vibrated. This movement of particles across the screens may be augmented by the conveyor action of the vibratory motor 49 when said motor is inclined as illustrated in Figs. 1 and 3. If desired, the axis of.

said motor 49 may be made substantially perpendicular to the average surface of the screens under which condition 'no appreciable conveyor action would be imparted by said motor 49. gravity alone then providing any conveyor action. I! desired, the axis of said motor 49 may be inclined to the planes of said screens at an acute angle opposed to the acute angle thereof illustrated in Figs. 1 and 3. Under these conditions, with the screens mounted at an angle as illustrated in Figs. 1 and 3, the conveyor action of the vibratory end, as it quite usually is, and the conveyor ac- ,tion of the motor 4! would be opposite a gravitational conveyor action on said material. If desired, the. screens may be placed substantially horizontal in which case the conveyor action of the material being screened will be due alm entirely to that of the motor ll.

' As a typical illustration of how the device of my invention may be employed. it may be stated that with said device supported, as illustrated in Figs. 1 and 2, material to bescreenedmaybe fed at the'upper end of the upper screen assembly ll. Said upper screen is generally appreciably coarser than the lower screen. *l'or'example, said upper screen may be a Ill-mesh screen and the lower as screen-may be a Ito-mesh screen. As the material to be screened passes downwardly across said upper screen under the vibratory movement thereof and under the combined conveyor action due to gravity and due to the motor 4!, those as particles which will pass the IO-mesh screen pass therethrough and fall onto the lower screen. Material' which is incapable of passing the lo-mesh screen will be discharged at the lower end of 'the upper screen' assembly II as, for example, into a hopper or receptacle. The material which passes through said upper screen and is received on said lower screen is subjected to another screening operation .and the constituent parts thereof which will pass through the lower screen,

through said lower screen and into a hopper or a receptacle placed beneath it. The fractions thereof which have passed the upper screen but aretoolargetopasslowerscreenwilibedischarged at the end of said] er screen into some kind of a receptacle or hopper.

Referring particularly to Fig. 4, there is i1- lustrated in sectional detail the particular construction of one means which may be employed to clamp the screen II or 2| to the end cylinder 2! or 22'. This means is duplicated for each screen and for each end of the device and thus a description of one will sufllce. A pair of angle members I02 and Ill is clamped together by bolts and nuts i I4 and clamp therebetween said screen '20. The lower of said angle members is extended at one side at III and is m'ovided along its length with a plurality of apertures I. Throughout the length of the pipe 22 extend a Q plurality oi' rods "Lone end of which is welded to the pipe 22 and the other end of which projects outwardly therefrom and is preferably hooked as at Ill. There is a rod I" for each of the apertures I" of the lower angle member Ill.

. Said apertures I" are adapted to be removably held to said pipe 22 by virtue of the hook portion III of said rods I". It is thus manifest that by rotating the pipe 22, the screen 2. will be wrapped about the surface thereof and tensioned. Adjacent the top of the channel member the spring leaves 83.

in the example given a 20-mesh screen, pass In Fig. 5, there is illustrated a alight modification of the screen clamping device illustrated in Fig. 4 which is particularly adapted to be used with fine mesh screens. This device differs from that of Fig. 4 in that the means for clamping the end of the screen 2. comprises a lower plate Ill and an upper channel member Ill adapted to carry a clamping'block 2, preferably formed of maple. Said'clamping members IIU, Ill and III are clamped together by a plurality of longi- 10 The tudinally-extending nuts and bolts 3. lower clamping plate Ill is provided with a plurality of longitudinally-extending apertures lll adapted to cooperate with the hooked endsof the rods lll'l. This-construction is preferred for II the fine screen because said screen is not bent at a sharp angle which might tend to break the strands thereof.

As was previously pointed out, the channel members 66 were rigidly attached to the field 20 structure of the motor I! and the armature .shaft 48 was rigidly attached to the armature thereof and upon energization of said motor 4!, there was relative movement between said armature shaft 48 and said angle members It. It 8' is manifest from the above description that the upper vibratory screen assembly I0 is rigidly at tached to the armature shaft 48 through the channel member 46 and the side plates 12 of said upper screen assembly I I and that the lower vithe upper vibratory assembly II and the lower 83 vibratory assembly II are flexibly attached by It is thus manifest that when said motor I! is energized, there will be a relative vibratory movement between the upper vibratory assembly II and the lower vibratory 4o assembly H. The period of this vibration will be determined by the frequency of the source which energizes the motor 49 andwill be twice this frequency.

The amplitude of vibration of the upper vibratory assembly with-respect to the lower vibratory assembly will, of course, be determined by the amplitude of vibration of said motor 49. This may be controlled by the adjustable means of said motor above described and may additionally be controlled by varying the amount of current flowing in the field winding of said motor as, for example, by controlling a variable resistor which may be inserted in the line of the field winding of said motor.

The distribution of'the energy between the upper vibratory assembly and the lower vibratory assembly and the consequent absolute vibration of each of these assemblies-that is, the

vibration of each assembly with respect to so space-may be proportioned 'as desired. This is effected by controlling the relative weights of each of the vibratory assemblies and all parts which are rigidly attached thereto and vibrate as a unit therewith. For example, if the upper as vibratory assembly and all the parts rigid therewith has a weight which is equal to that of the lower vibratory assembly and all the parts rigid therewith, each of the screen assemblies will have the same amplitude "of vibration and the energy of said motor 4,! will be equally divided between them. By making the weight of one of the vibratory assemblies greater than that of the other, it will have a smaller amplitude of vibration. That is, the absolute amplitude of vi- I bration of each of the screen assemblies in inversely proportional to the weight of said as-- sembly and the parts rigid therewith.

For most materials encountered in actual practice, it is desirable to provide greater amplitude of vibration for the upper screen assembly-Ill than for the lower screenassembly II. This is due to the fact that the raw material to be screened isfirst received on the upper screen 20 and thus there is a very large range of sizes of material on the upper screen. For example, the size ranges of the material may vary from zero to the maximum size of material received. This screen therefore has a difficult operaton to perform. The lower screen assembly need only operate on those sizes of materials which will pass the upper screen; thus its operation is less severe. For this reason, it is usual to design the relative weights of the upper and lower vibratory assemblies so that the upper vibratory assembly will have the greater amplitude of vibration. It

' may be desired to distribute the weight so the lower vibratory assembly will have the lesser weight and thus the greater amplitude of vibration. A typical example of where the upper vibratory assembly should preferab'iy have the lesser weight and thus the greater ampliture of vibration is when the upper screen 20 has a mesh of 10 and the lower screen 20' has a mesh of 50 and gravelranging from to. A inch is being treated, there being a large amount of material therein greater than-10 mesh. A typical example of where the upper vibratory assembly- I 0 should have the greater weight and thus' lesser amplitude of vibration is when the same size screens as above mentioned are employed and finished cement which has only a relatively few large impurities, such as broken machine parts, unground clinkers, etc. is being treated.

While it is not necessary to the operation of a my device, it greatly increases the efficiency of operation thereof and substantially reduces the amount of energy required to vibrate the screens, to proportion the weights of the vibratory structures so that, as a unit, they are effective under vthe action of the spring leaves II to have a natural period of vibration which is approximately the same as the frequency of vibration of the a motor 49.

Exact resonance is not necessary or even desirable and it is preferred that the natural period of said vibratory structures be slightly higher than the period of vibration of said motor 49. This means that there will always be some load on said motor 49 which providesdmproved control of the amplitude of vibration of the device and prevents any tendency of the device to destroy itself when vdoing no useful work. In addition, this allows some adjustment of the period of vibration of the vibratory structures to bring them nearer the resonance with the period of said motor by the simple expedient of slightly relieving the clamping compression on the spring leaves II.

It is, of course, obvious that the natural period of vibration of the mentioned vibratory structures axis of the motor 49. This condition should be maintained for any position of said motor 49 whereby the axis of vibration of said upper and lower screen assemblies I ll and II is substantially at right angle to the plane of said spring leaves 83. It is also to be noted that at least part of the reinforcing bars or channels 45 and 45' is parallel with the axis of vibration of motor 49.

While the motor 49 may beset at any desired angle with respect to the screens 20 and 20', where a conveyor action is desired, it has been found that this angle is preferably between 45 and-80 degrees with said screen surfaces 20 and 29' when this conveyor action is desired.

While the screen surfaces 20 and 20' are preferably substantially parallel as illustrated in the drawings, this construction is not absolutely essential and, if desired, they may be inclined at an acute angle-with respect to each other. For example, the lower screen20' might be mounted substantially horizontal while the upper screen 20 is inclined at an angle horizontal with the axis of the vibratory motor 49 either perpendicular to one of said screens or inclined to each of them. This construction will, of course, provide a different conveyor action of the motor 49 with respect to said screens 20 and 20' as the conveyor action of the motor with respect to each screen is determined by the angle the axis thereof makes-with said screen. j.

Obviously those skilled inthe art may make various changes in the details and arrangement of parts without departing from the spirit and scope of the invention as defined by the claims hereto appended, and I wish therefore not to be restricted to the precise construction herein disclosed.

Having thus described and shown an embodiment of my invention, what I desire to secure by Letters Patent of the United States is:

1. In a vibratory screening device, the combination with a pluralityof superimposed screens of different mesh carried by vibratory structures of difierent masses, of a vibratory electric motor for vibrating said vibratory structures and having an armature attached to vibrate with one of said structures and a field attached to vibrate with the, other of said structures, and flexible means supporting said screens and providing for movement of both which has a predominant vertical component. l

2. In a screening device, the combination with a pair of superposed screen decks, of means attaching said decks together for relative vibratory movement comprising members on opposite sides of one of said decks, a heavy flat vibrator spring extending between and attached at its ends to said members, means attaching the center of said vibrator spring to said other deck, an electromagnetic vibratory motor having an armature rigidly attached to one of said decks and a field structure attached to the other of said decks and operable at a predetermined frequency bearing a fixed relation to the frequency oi the operating alternating current, and means suspending said "screens to provide for their vibratory movement with a substantial verticalcomponent.

3. In a vibratory screening device, the combination with a pair of superposed screens of diiIerent mesh, of flexible means connecting said screens for relative movement, flexible means for supporting said screens to provide a horizontal component of movement of both of them, a vibratory electric motor constructed and arranled to vibrate at a fixed frequency predetermined by the frequency of the available commercial alterhating current, said motor comprising a field structure attached to one screen and an armature attached to the other, and a strong defiectable spring connected between said field structure and said armature and comprising a plurality a,

defiectable bars attached at their ends to said field structure and at their centers to said armature.

4. In a vibratory screening device, the combination with a pair of superposed screens of diiierent mesh, of flexible means connecting said screens for relative movement, flexible means for supporting said screens to provide a horizontal component of movement of both of them, a vibratory electric motor constructed and arranged to vibrate at a flxed frequency predetermined by the frequency of the available commercial alternating current, said motor comprising a field structure attached to one screen and an armature attached to the other, and a strong defiectable spring connected between said field structure and said armature. 1 v

5. In a vibratory screening device, the combination with a plurality of screens, of a straight line vibration type, of vibratory motor having an armature attached to one screen and afield structure attached to the other, said motor being operable to impart straight .line motion to said screens having a verticalcomponent, and means for flenbly supporting said screens to provide 'for the aforementioned straight line motion'of them.-

' JAMES A.'I"IJNT. 

